We are working on the analysis of gene activity, gene amplification, nucleic acid and protein synthesis in normal and infected larvae of insects (mainly sciarids). DNA synthesis is being studied at molecular and chromosomal levels. Larvae ofRhynchosciara have very large polytene chromosomes which attain supergiant sizes and show many physiological and/or structural changes in individuals infected with virus or microsporidia. Hormone injection in young normal larvae induces puffs, DNA amplification and a simultaneous initiation of synthesis in a great number of cells. These groups of cells initiate and terminate synthesis together. This phenomenon, added to the fact that all the larvae of a group develop synchronously, permit a detailed analysis of the still open problem of initiation and termination of DNA synthesis in chromosomes of eukaryote. As we did in Screw-worms we are no analyzing DNA duplication in embryonic cells of Musca domestica. In the present experiment we are making some embryos develop at 22 degrees and others at 37 degrees and analysing the effect of the temperature (at 37 degrees the embryos develop three times faster than 22 degrees) on the frequency of initiation sites and on the distance between them in spread molecules of DNA observed at EM. Other aspects of our research are described in section IV (Progress Report) BIBLIOGRAPHIC REFERENCES: Toledo, F. S. A., S. Y. Yang and C. Pavan. 1976. Isozyme analysis in two sibling Species of Rhynchosciara (Diptera, Sciaridae). Sciencia e Cultura 28:17-28. Juarand, A. and C. Pavan. 1975. Ultrastructural aspects of histolytic processes in the salivary gland cells during metamorphic stages in Rhynchosciara hollaenderi. (Diptera, Sciaridae). Cell differentiation 4: 2l9-236.